Descartes’ Substance vs. Hume’s Empiricism on Knowledge
The Evil Genius Hypothesis
The hypothesis is: Is an evil genius deceiving us and making us err in our own reasoning?
Metaphysics (Descartes): The Substances
Descartes arrives at the existence of three substances, each defined by an attribute:
- Thinking substance (res cogitans) (ego): Its attribute is thought.
- Infinite substance (res infinita) (God): Its attribute is perfection.
- Extended substance (res extensa) (bodies): Its attribute is extension.
Descartes defines substance as that which exists in such a way that it does not need anything else to exist. Strictly speaking, this definition only corresponds perfectly to the infinite substance (God) because it is the only one that needs nothing else to exist.
The conclusion for humans is that there are two separate substances: body and soul. These two substances that constitute man are heterogeneous, and their communication is something Descartes feels forced to justify. He refers to the pineal gland as the point from which the soul acts on the body, as if from a command post. Descartes ultimately recognizes that there is no clear and distinct idea regarding this question. The problem of substance would remain notably open for other philosophers.
Critique of Knowledge (Hume)
Hume is the philosopher who carried empiricism to its logical conclusion. He aimed to advance knowledge by building a single science: a science of man. He sought to achieve his objective by following empiricist principles and the inductive method of Newtonian science.
Hume inherits Locke’s empiricism in the sense that it is necessary to justify that our ideas are representations of reality.
Elements of Knowledge
Among the contents of consciousness, Hume recognizes two elements:
- Impressions: Perceptions that enter through the senses.
- Ideas: Representations or copies of impressions in thought. Ideas derive from impressions.
Hume admits that both impressions and ideas may be:
- Simple: They cannot be decomposed.
- Complex: They can be broken down.
Since there is nothing in our understanding beyond impressions or ideas, all contents of consciousness come from sensory experience: there are no innate ideas or abstract ideas in the understanding.
All of Hume’s radical empiricism is based on the distinction between impressions and ideas. This distinction determines a criterion of truth: an idea will be true if we can trace it back to the impression to which it corresponds. If this principle of correspondence between impressions and ideas is not met, Hume does not accept the truth of a concept. Consequently, experience is the origin and the limit of our knowledge.
Laws of Association of Ideas
Ideas are presented to our understanding in a certain order. This is because they associate according to certain laws. These laws are:
- Likeness
- Contiguity in time and space
- Causality (Cause and Effect)
Types of Knowledge
- Relations of Ideas: Although all ideas are based on impressions, we can establish relationships between them independently of reality. Therefore, there is no need to resort to experience to be certain that such a proposition is true. The relationship between ideas is independent of facts; propositions expressing them are analytic, universal, and necessary. Logic and mathematics belong to this type of knowledge.
- Matters of Fact: This refers to issues of fact,